https://www.migrationpolicy.org/article/spain-immigration-system-evolution?eType=EmailBlastContent&eId=a1fcdaaa-93ef-4a35-9397-e325534c6592&mc_cid=e4eef57c9d&mc_eid=d10a99d01e
https://www.opendemocracy.net/can-europe-make-it/john-weeks/trade-access-unemployment-and-other-single-market-mythologies?utm_source=Daily+Newsletter&utm_campaign=b26233dc76-DAILY_NEWSLETTER_MAILCHIMP&utm_medium=email&utm_term=0_717bc5d86d-b26233dc76-407405485
https://www.publications.parliament.uk/pa/cm201617/cmselect/cmintrade/817/817.pdf